Boeing XP-15

Last revised June 7, 1998




By the end of the 1920s, Boeing had realized that the biplane fighter was soon going to reach the end of the line, and that the monoplane held the key to the future. Rather than start with a radically new design, as had been attempted in the abortive XP-9, Boeing decided to adapt an existing design for its next monoplane fighter project. From the start, the project was a company-financed venture, with no promises of support from the military.

As first planned, the new Boeing design was merely the basic Model 89 (second prototype of the F4B/P-12 series) redesigned as a monoplane through deletion of the lower wing and the addition of struts to support the upper wing which was moved slightly aft to keep the center of lift in the correct position. This design was known by Boeing as the Model 97, but was not built. Following a decision to go to all- metal construction with a new fuselage design based on the XP-9 (Model 96), the designation was changed to Model 202. The reason for the large gap in company designations was due to the fact that company model numbers 103 through 199 had been reserved for Boeing-designed aerofoil sections.

The Model 202 that finally emerged was essentially a P-12/F4B with the lower wing removed and with a newly-designed parasol wing of increased wingspan attached to the fuselage by numerous struts. The wing was similar to that of the upper P-12 wing except for a 6-inch increase in span, the substitution of built-up dural spars and ribs for wood, and the use of dural skin for covering. The undercarriage was of split-axle design, and a tail wheel replaced the tail skid of the P-12. The portion of fuselage aft of the undercarriage rear attachment point was a semi-monocoque all-metal structure with dural formers, longitudinal stiffeners, and dural skin. The structure forward of this point was welded steel tubing covered with removable access panels and cowling. The original metal skin of the tail surfaces was smooth, but the second fin-rudder combination that was used was covered with corrugated metal. External tail bracing was similar to that of the biplanes. The undercarriage was of split-axle design, and a tail wheel replaced the tail skid of the P-12. The powerplant was the Pratt and Whitney SR-1340D Wasp air-cooled radial, rated at 450 hp at 8000 feet.

Since the Model 202 was a company venture rather than a military- financed project, it carried a civil registration (X-270V) rather than a military serial number.

The Model 202 flew for the first time in January of 1930. The shape of the vertical tail was changed to that eventually standardized for the later P-12E and a ring cowl similar to that installed on production P-12Cs was added before the XP-15 was sent to Wright Field. The military designation of XP-15 was assigned unofficially when the USAAC accepted the Model 202 at Wright Field for flight test under a bailment contract on March 10, 1930.

During tests at Wright field, the XP-15 attained a maximum speed of 163 mph at sea level and 190 mph at 8000 feet. The initial climb rate was 1800 ft/min at 800 feet. Service ceiling was 26,550 feet and range was 421 miles. Weights were 2052 lb empty, 2746 lb gross. The aircraft was to have been armed with two 0.30 cal machine guns, but these were never actually fitted.

The deletion of the lower wing increased the top speed of the XP-15 over that of the P-12B, but the rate of climb, the maneuverability, and the landing speed all suffered from the decrease in wing area. Consequently, the design was not accepted for production by the military, and the Army never actually purchased the XP-15 prototype. Therefore, it was never assigned a USAAC serial number.

The XF5B-1 was an almost identical duplicate of the Model 202 that had been ordered for the US Navy. It differed mainly in being fitted for operation from aircraft carriers as a fighter-bomber. An arrester hook was fitted. The engine was a supercharged Pratt and Whitney SR-1340C offering 480 hp at sea level. The company designation for this aircraft was Model 205. The Model 205 was delivered to the Navy in February 1930. Like the Model 202, it was originally tested by the Navy under a bailment contract and bore the civil registration X-271V. By the time that test flights were terminated at the beginning of 1932, it had been decided that the monoplane still did not have the reliability needed for a successful carrier-based airplane. Although the Navy did not accept the aircraft as a production type, they nevertheless purchased the airplane and the designation XF5B-1 became official. The serial number was A-8640. After three years of testing, the airframe was static tested to destruction.

After return to the factory from Wright Field, the XP-15 was used for further test and development work, in the vain hope that it might eventually be granted an Army contract. However, all such hopes were dashed on February 7, 1931, when the XP-15 crashed near Seattle after a propeller blade failed during a vertical climb following a high speed run. The resulting vibration shook the engine out of the airframe. The program was abandoned shortly thereafter. Although the aerodynamic design was not accepted by the Army, many of the structural features of the XP-15 were incorporated into later models of the P-12/F4B series then in production.

Sources:

  1. Boeing Aircraft since 1916, Peter M. Bowers, Naval Institute Press, 1989.

  2. "Boeing F4B-4", Peter M. Bowers, in "Aircraft in Profile", Doubleday, 1969.

  3. United States Military Aircraft Since 1909, Gordon Swanborough and Peter Bowers, Smithsonian Institution Press, 1989.

  4. The American Fighter, Enzo Angellucci and Peter Bowers, Orion Books, 1987.